Make your first test code, in a file called FirstTest.java
Add these imports:

import static org.junit.Assert.*;
import org.junit.*;

Here is the remainder of the class:

// Needs to be public
public class FirstTest {
// Needs one constructor that takes no parameters
public FirstTest() {
}
// Use the @Test annotation and call it should*
@Test public void shouldDoSomething() {
// Do some tests...
int i = 3;
// Use the assert* methods
assertEquals(3, i);
assertNotNull(i);
assertTrue(i == 3);
}
}